The resonator fiber optic gyroscope (RFOG) has been developed to meet the needs of many navigation and inertial stabilization markets. The current RFOG designs now being developed involve having at least two laser beams that co-propagate through a rotation sensing coil. Since the two laser beams are at different frequencies and have different modulations applied to them, beat notes generated by the beams mixing on the same photodetector produce a very complex signal spectrum that makes it difficult to detect the desired signal. These complications lead to performance degradation. Furthermore, some designs involve four lasers, which lead to additional complexity.
In some current RFOG implementations, three lasers are employed, including one master laser and two slave lasers. The master laser is stabilized to a reference resonator that is different from the gyroscope resonator. Differential frequency noise between the reference resonator and the gyroscope resonator can limit the RFOG performance. Another disadvantage of this approach is that it requires an additional resonator, thus adding complexity, size, weight, and cost to the RFOG.
Other RFOG implementations combine a component of the master laser light with one of the slave laser beams so that the master can be stabilized to the gyroscope resonator. This eliminates the issues associated with having an independent reference resonator, but introduces the signal complexity issues with having the master and slave lasers mix on the same detector used for resonance tracking and rotation sensing.
Another issue with conventional RFOG designs is that resonance probing in the clockwise direction and the counter-clockwise direction is not symmetric, which can lead to rotation sensing errors.
Accordingly, there is a need to eliminate co-propagating laser beams while maintaining a symmetric RFOG design.